The invention relates to a process for the preparation of polyoxyalkylene ethers of the formula EQU R.sup.1 O--[C.sub.n H.sub.2n O--].sub.x M
in which
R.sup.1 is an alkyl radical with 1 to 4 carbon atoms, an alkylene radical, an aryl radical or an alkaryl radical, PA1 M is an alkali cation, PA1 n is any number from 2 to 3, and PA1 x is a whole number, PA1 R.sup.2 is hydrogen or a methyl radical, PA1 n is any number from 2 to 3, and PA1 x is a whole number, and which has a narrow molecular weight distribution. The distinguishing feature of this process is that the polyoxyalkylene ether having the formula R.sup.1 O--[C.sub.n H.sub.2n O--].sub.x M is first synthesized by the stoichiometric polymerization of alkylene oxides or their mixtures of the general formula C.sub.n H.sub.2n O on alkali alcoholates of the general formula MOR.sup.1, in which M is an alkali cation, at temperatures of 60.degree. to 130.degree. C. This intermediate product is then reacted with an allyl or methallyl halide in a well known manner and the product is separated from the salt MX which is formed as a by-product. PA1 R.sup.1 is an alkyl radical with 1 to 4 carbon atoms, an alkylene radical, an aryl radical or an alkaryl radical, PA1 M is an alkali cation, PA1 n is any number from 2 to 3, and PA1 x is a whole number,
by stoichiometrically polymerizing alkylene oxides or their mixtures having the general formula C.sub.n H.sub.2n O on alkali alcoholates having the general formula MOR.sup.1 at temperatures of 60.degree. C. to 150.degree. C. 2. Description of the Prior Art
German patent application No. P 31 21 929.2 describes a process for the preparation of polyoxyalkylene monoallyl or methallyl ethers of the general formula ##STR1## in which R.sup.1 is an alkyl radical with 1 to 4 carbon atoms, an aryl radical or an alkaryl radical,
Accordingly, in the first step of this process, an alkylene oxide of the formula C.sub.n H.sub.2n O is added to stoichiometric amounts of an alkali alcoholate of the general formula MOR.sup.1 in a conventional manner. As used herein, stoichiometric amount means the amount of alcoholate which is equivalent to the number of resulting polyoxyalkylene chains, so that each individual chain is started by an alkoxy anion and each chain has an alkali ion.
It was, however, surprising that in spite of the use of large amounts of alkali alcoholates, the isomerization of propylene oxide to allyl alcohol, which is well known as such and to be expected, takes place to only a very slight extent. Also, the intermediate products obtained in the first step of the process have only a low double bond content. This isomerization of propylene oxide, which is to be expected, is largely avoided especially when the propylene oxide, optionally in admixture with ethylene oxide, is added to sodium methylate at temperatures up to 100.degree. C.
In carrying out this step of the process, it turns out that delays in the addition reaction of the alkylene oxide are observed now and then. The alkylene oxide supplied to the reactor, does not initially add on, so that as more alkylene oxide is supplied, the amount of unreacted alkylene oxide in the reactor increases until the reaction then starts and, due to the heat of reaction released, accelerates and proceeds explosively. Consequently, due to the temperature and pressure increase in a reaction which starts so suddenly, disturbances in the molecular weight distribution and the composition of the reaction products may occur. Also, a reaction which starts so precipitously, can endanger the operating personnel.
Such delays in the onset of the reaction occur especially in the temperature range up to about 100.degree. C. If the reaction temperature is raised to about 120.degree. to 130.degree. C., the tendency for such reactions to be delayed is reduced. However, a higher reaction temperature favors the formation of products of relatively lower molecular weight, so that the hydroxyl number found is larger than the theoretically calculated hydroxyl number of the product. Moreover, the isomerization to allyl alcohol is favored when propylene oxide is used as the alkylene oxide.